Strata

Strata (singular: stratum) are layers or beds of material that possess relatively uniform properties and are distinct from adjacent layers. The term is used in several disciplines to describe a layered structure in which the layers, or strata, are arranged in a specific order and can often be distinguished by composition, texture, color, or other characteristics.

In geology and earth science, strata are successive layers of sedimentary rock or soil formed by deposition over time. Bedding planes separate strata and indicate changes in deposition. The study of strata, stratigraphy, uses fossil content and rock characteristics to interpret past environments and to establish relative ages through principles such as superposition and fossil correlation.

In sociology and anthropology, strata refer to social layers within a population, forming a stratified society. Strata are defined by variables such as income, occupation, education, or ethnicity, and they influence access to resources, opportunities, and life chances. Social mobility measures movement between strata.

In biology and medicine, the term describes tissue organization. Stratified epithelia consist of multiple cell layers; the most familiar example is stratified squamous epithelium, which provides protection for the skin, mouth, and esophagus. This arrangement contrasts with simple epithelia, which have a single cell layer.

In mathematics, a stratified space is decomposed into strata, each a smooth manifold of a fixed dimension, arranged to satisfy certain regularity conditions. This framework helps study spaces with singularities, such as orbit spaces and algebraic varieties, by organizing them into more manageable pieces.